Description: This solution discusses how to import an additional address as an alternate without overwriting the existing address record.
This would require you to map the address type and preferred status. In order to do that you would need to map Constituent > Address > Preferred and Constituent > Address > Type. As seen below. Then have the incoming address type from the data file, set to the desired type and the incoming preferred status from the data file, set to NO.
For additional information, please refer to the ImportOmatic User Guide